The present invention relates to a core of a magnetic head, and more particularly to a structure of a magnetic head core made of ferrite which is easy to manufacture and excellent in quality. The present invention is also concerned with a composite magnetic head core which consists of two ferrite cores bonded together.
In the art of magnetic heads, a core made of ferrite has been known, which generally consists of a pair of ferrite core elements joined together to form a structure of ring-shaped or toric cross section having a centrally located aperture or opening which facilitates winding of coils around the core elements. More specifically stated referring to FIG. 1 which shows a common type of magnetic head core, a pair of generally C-shaped ferrite core halves 2, 4 are butted together to form the core with a central aperture 6 which serves as a space for winding coils 8 around the core halves 2, 4. In this manner, an generally annular or toric magnetic path (magnetic circuit) is constituted by the two C-shaped ferrite core halves 2, 4. Additionally, the toric magnetic core structure is formed with a magnetic gap 10 at one end portion of the core. The gap 10 is formed to extend across the torus of the toric magnetic circuit and has a suitable width .alpha.. As is well known in the art, a magnetic tape 12, magnetic disk or other magnetic recording medium is slidably moved on outer contact surfaces on the core halves 2, 4 in the proximity of the magnetic gap 10 defined by these two halves 2, 4, whereby magnetic recording (writing) and reproducing (reading) operations are executed. As indicated above, the ends of the core halves 2, 4 at one end of the core define the magnetic gap 10, while the other ends of the core halves 2, 4 are bonded together with suitable bonding glass so as to maintain a generally annular or toroidal cross sectional shape of the magnetic core as a whole. In this manner of bonding of the core elements 2, 4, it is inevitable that a very small gap, so called a rear or back gap 14, is formed between the bonded surfaces of the core elements 2, 4.
In such a ferrite core as described above, a writing, reading or erasing track or tracks of a suitable width is/are provided on the contact surface on which a magnetic recording medium (12) is moved in sliding contact, i.e., on the outer surfaces of the opposed end portions of the two ferrite core elements 2, 4 in the vicinity of the magnetic gap 10. The track is formed so as to extend in the direction of movement of the recording medium. The width of the track is selected depending upon the specific magnetic recording medium (12) used. In a commonly known ferrite core, the width of the track is usually defined or determined by a central or middle groove or side grooves formed in the opposed end portions of the core elements 2, 4 defining the gap 10. The middle groove is located in the middle of the contact surface as viewed in the width direction perpendicular to the direction of sliding movement of the recording medium, so that two tracks are formed on both sides of the middle groove. On the other hand, a single track is defined by two side grooves which are formed on both sides of the track.
Examples of such grooves are shown in FIGS. 2(a) and 2(b), wherein two side grooves 16, 16 are formed in the opposed portions of the core elements 2, 4 which are located on both sides of the magnetic gap 10 to define the gap 10. The two side grooves 16, 16 define therebetween a track 18 having a suitable width w as measured perpendicularly to the direction of sliding movement of a magnetic recording medium. The two side grooves 16, 16 are filled with masses of glass 20 in order to protect the track 18 and its vicinities, and prevent otherwise possible breakage, chipping or similar damage to the corner portions defining the grooves 16, 16.
In this type of ferrite core wherein the grooves 16, 16 determine the width w of the track 18, the grooves 16, 16 are formed in each of the opposed end portions of the elements 2, 4 defining the magnetic gap 10 over a sufficient length. Further, each of the core elements 2, 4 should be processed, prior to bonding thereof, to provide two cutouts which eventually form the grooves 16, 16 when the elements 2, 4 are bonded together. This requires a cutting process to be done in each of the individual core elements 2, 4, and needs accurate control of the widths of the cutouts and the spacings between the cutouts in each core element 2, 4, so that the two halves of the track 18 are exactly aligned with each other to provide the predetermined width w on both of the core elements 2, 4.
In the above case wherein the two core elements 2, 4 are subjected to cutting operations to form the individual cutouts for the grooves 16, 16, it is required to precisely position the two elements 2, 4 upon bonding thereof to form an integral core structure, such that the two halves of the track 18 defined by the grooves 16, 16 are accurately aligned with each other. This alignment is a difficult and cumbersome step in the conventional process of manufacturing a known ferrite core. In other words, inaccurate relative positioning of the two core elements 2, 4 results in relative misalignment of the two halves of the track 18 at the interface of the core elements 2, 4 as illustrated in FIG. 2(c), thus leading to reduced quality of the ferrite core.
There is also known a ferrite core as shown in FIG. 2(d). Unlike the above-discussed ferrite core having the grooves 16, 16, this ferrite core has side grooves 22, 22 which are cut to extend along the length of the track 18. These parallel grooves 22, 22, are formed after the two core elements 2, 4 are bonded together. Thus, the grooves 22, 22 define a track 18 having a suitable width w and a desired length. However, since the grooves 22, 22 on both sides of the track 18 should have a depth sufficient to reach the coil-winding aperture 6, the uncut portions (lands) of the core elements 2, 4 providing the track 18 and defined by the deep parallel grooves 22, 22 tend to have a large height relative to its width. Stated differently, it is difficult to form the track 18 as designed, by cutting such deep parallel grooves without breakage or chipping of the uncut portions. This problem is aggravated as the width w of the track 18 is reduced. While the side parallel grooves 22, 22 defining the track 18 are filled with glass 20, as in the examples of FIGS. 2(a) and 2(b), it is recognized as another drawback that the glass 20 in its molten phase will easily flow down over the side end surfaces of the core elements 2, 4 beyond the longitudinal ends of the grooves 22 in the direction along the length of the track 18. Thus, the ferrite core of FIG. 2(d) has various drawbacks in its process of manufacture.
A ferrite magnetic head core as described above is used either alone, or as one of two elements of a composite maganetic head core which consists of a pair of such ferrite cores. Some examples of a composite core are illustrated in FIGS. 3(a) through 3(d). Each of the composite cores shown in FIGS. 3(a) and 3(b) is a composite which consists of a ferrite writing head core 106 consisting of an integral assembly of a C-shaped core element 102 and a rectangular core (I-shaped core) element 104, and a ferrite reading head core 108 consisting of another integral assembly of the same core elements 102, 104. FIGS. 3(c) and 3(d) show composite cores each of which is a composite of a ferrite writing/reading head core 110 and a ferrite erasing head core 112, each core 110, 112 consisting of core elements 102, 104 which are similar to the core elements 102, 104 of the ferrite cores 106, 108 of FIGS. 3(a) and 3(b).
Each of the ferrite cores 106, 108, 110 and 112 has a magnetic gap 114 defined by opposed end portions of the core elements 102, 104 which provide contact surfaces on which a magnetic recording medium is moved in sliding contact. These contact surfaces on the opposed end portions in the vicinity of the magnetic gap 114, that is, the outer surfaces of the opposed end portions on both sides of the magnetic gap 114, is formed with a track or tracks 116 which extend in the direction of sliding movement of the magnetic recording medium, so that the recording medium moves in sliding contact with the tracks 116 for magnetic writing and reading operations. The width w of the tracks 116 is determined depending upon the specific kind of the recording medium. In known writing and/or reading head cores indicated at 106, 108, 110, the width of the track 116 is determined by two side grooves 118 which are formed in the opposed end portions of the core elements 102, 104 on both sides of the magnetic gap 114 such that the grooves 118 are located on both sides of the track 116 to define the track 116 therebetween, i.e., in the middle of the width of the contact surfaces as measured in the direction perpendicular to the direction of sliding movement of the recording medium. In erasing head cores as indicated at 112, a middle groove (recess) 118 is formed in the middle of the width of contact surfaces through the opposed end portions of the core elements 102, 104 so that the middle groove 118 defines the two tracks 116 on both of its sides. The side grooves 118 or the middle groove 118 are/is filled with glass 120 to protect the track or tracks 116, and prevent breakage or chipping of corner portions of the grooves. In each of the ferrite cores 106, 108, 110 and 112, a coil-winding aperture 122 is formed between the core elements 102, 104.
In the aforementioned composite magnetic head cores wherein the middle groove 118 or side grooves 118 define the width w of the track or tracks 116, the grooves 118 are formed in both of the opposed portions of the core elements 102, 104, over a relatively long distance. Further, all of the core elements 102, 104 should be processed, prior to bonding thereof, to form recesses or cutouts which eventually form the grooves 118 when the core elements 102, 104 are bonded together. This requires repetitive cutting operations on the individual core elements 102, 104, and requires accurate control of the widths of the recesses and spacings between the recesses, so that the two halves of each track 116 are exactly aligned with each other to provide the predetermined width w on both of the core elements 102, 104.
An exemplary process of manufacturing ferrite cores used to form a composite magnetic head core as introduced above is disclosed in Japanese Patent Aplication laid open in 1976 under Publication No. 51-96308. This process comprises the steps of: cutting slanted or straight grooves in each of a pair of ferrite core elements in the form of blocks; melting a glass material to fill the grooves with the molten glass; finely grinding surfaces of the core elements defining a magnetic gap; cutting a groove in one of the core elements so as to define a central aperture for winding coils; applying a layer of glass of a suitable thickness, with a sputtering method, to at least one of the surfaces defining the magnetic gap; assembling the two core elements in a mutually abutting relationship; and heating the assembly to bond the two core elements to obtain an integral ferrite core structure. Thus, ferrite core structures are produced. Then, a pair of these core structures are bonded together with bonding glass, whereby a desired composite magnetic head core is manufactured.
Such a known manufacturing process as described above, however, is very complicated and cumbersome. Apparently, the individual grooves or cutouts formed in the core elements should be accurately cut to tight dimensional tolerances. Further, the processed core elements with the grooves should be precisely aligned with each other upon assembling the blocks in a mutually abutting relationship. This is also an extremely troublesome and difficult step. If the relative alignment of the core elements is not sufficiently accurate, two halves of each track 116 are displaced laterally from each other as depicted in FIG. 3(e). This alignment error will reduce the quality of the ferrite cores, and consequently results in degrading the quality of the composite core using the ferrite cores. In addition, even if the core elements are accurately aligned with each other, it is further necessary to accurately align the two ferrite cores, otherwise the tracks on one of the ferrite cores are not aligned with the tracks on the other ferrite core as shown in FIG. 3(f).
Also known in the art is a ferrite core which is formed with grooves 124 which, unlike the above discussed grooves 118, are formed in parallel with the track 116 as shown in FIG. 4.
This ferrite core is produced by bonding two ferrite core elements 102, 104 into an integral assembly, and then cutting the grooves 124 in the opposed portions of the core elements 102, 104 defining magnetic gaps 114, such that the grooves 124 are formed on both sides of and in parallel with the track 116 in order to define the track 116 with a desired length and a desired width w. Since these grooves 124 should have a depth sufficient to reach a central coil-winding aperture 122, the uncut portions (lands) of the core elements 102, 104 providing the track 116 and defined by the deep parallel grooves 124 tend to have a relatively large height relative to its width, as previously indicated in association with the grooves 20 of FIG. 2(d). In other words, it is hard to form the track 116 as intended, without breakage or chipping of the uncut portions during the cutting of such deep grooves. This problem is serious when the width w of the track 116 is relatively small.